Actually, the definitions you quoted are no more abstract than necessary and
are admirably realistic; that is, reflective of the actual usage of these
words (unlike the absurd and prejudiced characterization from the "ethics
class").
Check the definitions again (**'s and [...] mine):
From EB's Webster Online dictionary:
pornography
1 : the depiction of erotic behavior (as in pictures or writing)
**intended to cause sexual excitement**
2 : material (as books or a photograph) that depicts erotic
behavior and is **intended to cause sexual excitement**
3 : the depiction of acts in a sensational manner so as to **arouse a
quick intense emotional reaction**[ie, provoke a reaction analagous to
sexual arousal] <the pornography of violence>
erotica
1 : literary or artistic works **having an erotic theme or quality**
2 : depictions **of things erotic**
The difference -- and, as you note, it doesn't preclude overlap -- is that
one term identifies a type of tool, and the other a class of art/popculture
works...
Mike